Curable fluorinated elastomer compositions utilizing addition reaction between alkenyl and hydrosilyl groups are well known in the art. These compositions can be rendered self-adhesive by adding an organopolysiloxane having a hydrosilyl group and an epoxy and/or trialkoxysilyl group as the third component, as disclosed in JP 3239717 and JP 3567973. These compositions may cure on brief heating into elastomers having advantages including solvent resistance, chemical resistance, heat resistance, low-temperature properties, low moisture permeability, and electric properties. They are used in the adhesive application in various industrial fields where such properties are required, and frequently for the bonding and sealing of electrical components in the automotive industry.
These compositions are useful as a durable bonding/sealing agent capable of utilizing stress relaxation of elastomer, when applied between materials of like or different type. However, problems arise when these compositions are applied for coating of electric/electronic component-loaded boards and for potting of electric/electronic component-receiving packages. As the coating weight or casting amount increases, the surface of cured products tends to deviate from smoothness and become non-uniform or irregular. Then dust, soot, water, corrosive substances or the like accumulates in surface dimples. Such deposits become starting sites for decomposition reaction, resulting in local variations of protection performance. To solve the problems of the above compositions (JP 3239717 and JP 3567973), JP-A 2005-002142 and JP-A 2007-126496 propose to add thereto an isocyanurate compound having at least one epoxy and/or trialkoxysilyl group bonded to a nitrogen atom via a carbon atom in a molecule. The resulting compositions are fully adherent to a variety of substrates including metals and plastics and form protective members (cured products) having a smooth and uniform surface independent of their thickness. They still have the drawbacks that the cure rate largely varies depending on the amount of the isocyanurate compound added, and curability lowers with time during shelf storage.